The unique two-dimensional spatial structure gives graphene excellent chemical and physical properties and huge specific surface area. These make graphene a very promising material for energy storage applications. This paper reviews recent progress in the use of graphene in chemical energy storage, including hydrogen storage, supercapacitor, lithium ion batteries, lithium-sulfur batteries and lithium-air batteries. Relationships between different preparation methods of graphene and their chemical/electrochemical properties are discussed. Graphene could form three dimensional conductive network to enhance the electrochemical properties of electrodes materials, but also provide a buffer for the volume change during charging-discharging processes to extend the life-span. Further improvements of electrochemical performance are able to be achieved by optimizing the microstructure of composite materials. Finally, key issues related to practical applications of graphene are briefly discussed.

This bimonthly review paper highlights 90 recent published papers on lithium batteries. We searched the Web of Science and found 971 papers online from Dec. 1,2013 to Jan. 31,2014. 90 of them were selected to be highlighted. Layered oxide and high voltage spinel cathode materials are still under extensive investigations. Large efforts were devoted to Si based anode materials and composite carboneceous anode, additives for electrolyte. There are few papers related to Li-S battery, Li-air battery and more papers related to theoretical simulations, cell analyses and modeling.

This paper attempts to assess the use of energy storage systems (ESS) for recovering and reusing braking energy in urban rail transportation systems from an economic point of view. Capital and maintenance costs are taken into account. The results suggest that a hybrid energy storage system using battery and ultracapacitor be an optimal mode both in terms of the economic considerations and the response time.

SnO₂/C composites were synthesized by a reflux-assisted hydrothermal method using SnCl₂·2H₂O and polyvinylpyrrolidone (PVP) as raw materials. Crystalline structures and morphology of the composite particles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrochemical performacne of the composites were evaluated using Galvanostatic charge-discharge, electrochemical impedance spectrum (EIS) and cyclic voltammetry (CV) devices. The results showed that the SnO₂/PVP composites could deliver a reversible discharge capacity of 591.7 mA·h·g^-1 after 100 cycles, indicating an excellent cycling performance. High extent of dispersion of SnO₂ nanoparticles (5~10 nm) in amorphous carbon and good buffering effect to absorb the volume change of tin particles during the charging/discharging process were proposed to be the main reasons for the observed high material performance.

Adipic acid-amorphous silica composite phase change thermal energy materials are prepared by using a hydrothermal method. The composite materials are characterized by X-ray diffraction (XRD), Fourier transformation infrared spectroscopy (FT-IR), field emission scanning electron microscope (FE-SEM), and synchronous thermal gravimetric analyzer (TGA) and differential scanning calorimetry (DSC). The results show no sign of chemical reactions between adipic acid and silicon dioxide at pH of 5 and temperature of 150 ℃. The particle size of the composite phase change material is uniform with 1--2 μm diameter. The phase change temperatures and the latent heats of the composites are respectively 139.0 ℃ and 48.82 J/g for 30% (by mass) adipic acid loading and 140.5 ℃ and 71.89 J/g for 50% (by mass) adipic acid loading.

Paraffin-water emulsions were prepared by using a phase transformation emulsification method. Span80 and Tween80 were used as the emulsifiers. Paraffin content up to 40% could be obtained by using such a method. The emulsions were characterized for their viscosity and latent heat by using the NDJ-1 viscometer and the Q10 differential scanning calorimeter (DSC), respectively. The results showed that uniform and stable paraffin wax emulsions could be obtained when the HLB of emulsifiers was about 10 (i.e. the weight ratio of Span80 to Tween80 was round 46.8∶53.2). The viscosity of the emulsions increased sharply with increasing wax content, whereas the latent heat was at maximum when the oil and water phases coexisted. When the emulsion contains the oil phase only, the latent heat increased with increasing water content, while the latent heat of the emulsions decreased with increasing water content when the emulsion contains the water phase.

This study aims to develop a paraffin-based phase change material (PCM) emulsion with a low extent of supercooling for thermal energy storage (TES) systems to improve the cooling efficiency. Hexadecane-water emulsions were prepared and characterized. Multi-wall carbon nanotubes (MWCNTs) were dispersed in the emulsion as a nucleating agent to reduce the supercooling. The MWCNTs were chemically modified with carboxyl groups to improve the dispersion of the tubular particles in the organic liquid. Thermal analyses of the emulsions by differential scanning calorimeter (DSC) indicated that the extent of supercooling was significantly reduced. The concentration of the nucleating agent for an effective supercooling suppression as found to be very low, in agreement with previous findings, and there appeared to be a minimum concentration for the supercooling reduction.

For crude oils with a high solidifying point, freezing can easily occur when the flow is stopped. Determining the maximum stopping time is therefore crucially important for safe rebooting of the system. This stopping time depends on the heat storage capacity of crude oil, heat transfer conditions of the pipeline system and surrounding soil temperature field. This paper reports a numerical study on the unsteady state heat transfer of an oil transportation line under the stopping conditions. The results indicate a strong natural convection in the crude oil and the temperature of crude oil in pipeline drops rapidly in the initial stage of the stopping transportation, and the temperature decrease slows down with time. Such a change in the time dependence of temperature is related to the change of heat transfer mode from natural convection and conduction in the initial stage to conduction in the late stage. For the conditions considered in this work, the oil temperature drops to 38 ℃ after 21 hours, suggesting the stopping time should not exceed 21 hours.

Vanadium flow battery systems consist mainly of membrane separators, electrode plates, electrodes, electrolyte storage tanks and circulation pumps. Energy storage is realized through changes to vanadium ion valence states in the charge and discharge processes. In this study, effects of vanadium electrolyte concentration and temperature on the electrochemical cyclic voltammetric behavior are investigated. The results show that, for a given temperature, the number of ions participating in the electrochemical reactions increases with increasing vanadium ion concentrations, leading to an increased output current. However, the reversibility of electrochemical reaction becomes poorer with increasing vanadium ion concentration. For a given vanadium concentration in the electrolyte, the peak current due to oxidation and reduction reactions increases with increasing temperature. The results also show that the current density of the electrochemical reactions could be increased by increasing the temperature of vanadium electrolyte within a certain range. For a given vanadium concentration in the electrolyte, the sulfuric acid concentration is also an important factor with 3 mol/L giving a good performance of vanadium electrolyte.

Successful commercialization of lithium ion batteries originated from the development of petroleum coke based anode materials by SONY in 1991. Anode materials play a key role in the progress of lithium ion batteries. Up to now,carbon, lithium titanate and alloy anode materials have been commercialized. Li-ion batteries using conventional carbon anode materials can more or less meet the requirements of consumer electronics, electric vehicles and large scale energy storage applications. Lithium titanate anodes can meet high power density applications such as electric buses, whereas the use of alloy anodes can further improve the energy density of Li-ion batteries. In this paper, we summarize briefly the characteristics of anode materials that have been commercialized and widely used, and discuss developments of next generation anode materials.

All-vanadium redox flow batteries (VFBs) are made of a series of single cells connected in parallel and packaged into a stack. A common channel connects single cells and distributes positive or negative electrolyte into each cell. Due to the electric potential in the stack, vanadium ions migrate along a specific direction in the positive or negative electrolyte that flows through the common channel, leading to the formation of shunt current and hence energy loss. This paper analyses the causes of shunt current formation, develops a mathematical model based on the analyses, and provides strategies to constrain the formation of shunt current. It is found that the formation of shunt current and hence the associated energy loss can be effectively reduced through a proper design of the flow channels.